This invention relates to extracting and purifying cobalt from aqueous solutions containing cobalt and other metal values.
There are many hydrometallurgical processes for extracting metal values from ores that contain several metals, such as copper, nickel and particularly cobalt, in which the metals are first leached from ores and then are subjected to successive separations to separate the metals values. In some processes, cobalt is placed into organic phase by an organic extractant, stripped from the organic phase by an aqueous acid and the metal is recovered by electrowinning. An example of this type of process is disclosed in Chemical Engineering, Nov. 3, 1980, pp. 43-45. Similar processes are disclosed in Bureau of Mines Report of Investigation/1980, RI 8419 and U.S. Pat. No. 4,083,915.
U.S. Pat. No. 4,258,016 teaches the use of liquid ion exchange using LIX 51.RTM., a commercial mixture of betadiketones, as organic extractant, and the use of sulfuric acid to strip the pregnant LIX 51 of cobalt to create a suitable cobalt electrolyte. Cobalt values are stripped from the organic extractant by sulfuric acid.
U.S. Pat. No. 3,988,151 discloses a process to recover copper and nickel values from an aqueous solution containing both values by first extracting copper into an organic phase and then extracting the nickel into an organic phase, and subsequently stripping the nickel containing organic solution with an aqueous strip solution of ammonia and carbon dioxide.
Cobalt was considered incompatible with this particular system since it was believed that cobalt poisoned LIX 64N.RTM..
A portion of the ammonia tends to transfer into the organic phase with the cobalt values. This causes a loss of ammonia from the aqueous system. An equivalent amount of ammonia must be added to the leach system to make up for this loss. In addition, the ammonia present in the organic phases causes consumption of acid during the acid stripping step, beyond that which is required to recover the cobalt. Both the ammonia loss and extra acid consumption constitute undesirable economic penalties. Furthermore, during such a process, various insoluble ammonium-containing salts, such as ammonium cobalt sulfate, can form and lead to significant operating problems.
A particularly attractive source of cobalt is spent hydroprocessing catalysts. Cobalt alone, or in combination with other metals, particularly molybdenum, is frequently a component of hydroprocessing catalysts. Due to the high cost of cobalt, and the uncertainty of continuing supply, it is highly desirable to recycle cobalt recovered from deactivated hydroprocessing catalysts to manufacture of fresh catalysts. Since cobalt is usually placed in the catalyst support, as a soluble solution of a cobalt salt, such as cobalt oxide or cobalt carbonate, the isolation of pure cobalt metal, by electrowinning, is an unneeded step. The soluble salt of the metal is a preferable source of cobalt for the production of catalysts.
Hydrocarbonaceous feedstocks, for example crude oils, vacuum and atmospheric residua, topped crudes and the like, are frequently contaminated with metals, including nickel, vanadium and iron, bound to organic molecules, for example, phorphorins, and are removed by contacting the feedstock with hydroprocessing catalysts. During hydrodemetalation, the metals tend to deposit on the surface of the catalyst pores, eventually plugging them and deactivating the catalyst. Such deactivated catalysts can be viewed as an ore that is very rich in cobalt, nickel, vanadium and molybdenum.
It would be advantageous to hydroprocessors and hydroprocessing catalyst manufacturers if a process were found for extracting cobalt from aqueous solutions without the disadvantageous features of the prior art.